This invention relates generally to test instruments for local area networks (LANs) and in particular to a method for determining the relative health of a LAN.
Increasingly complex LANs, or simply "networks", now connect more and more types of devices including personal computers, work stations, file servers, and printers. Network hubs are often the central devices in a network through which information flows. Each client device connects to the LAN via adapters called network interface cards (NICs) to form nodes. Connecting the nodes to the hubs are network links which may consist of unshielded twisted pair (UTP) wire, coaxial cable, or fiber optic cable.
Network protocols for controlling the communication of information between the nodes have been developed, the most common being Ethernet or 10BASE-T which is defined according to the IEEE 802.3 standard. Ethernet has a speed of 10 megabits per second and uses a media access protocol called carrier-sensing multiple access with collision detection (CSMA/CD) to control information traffic flow and resolve collisions between nodes. A node can send information on the network only if no other node is currently sending information. If a node tries to send information at the same time as another node, a collision occurs and each node operates according to a well-defined "back off" procedure to resolve the collision. Each node will wait a random period of time to attempt to send the information again.
Because Ethernet is typically implemented in a baseband, broadcast network, every node receives the information sent by every other node within the collision domain. In order to minimize the burden on the software operating in host personal computers (PC's) connected to the network, a hardware layer with a hardware or media access control (MAC) address passes along to the software layer only the information appropriate for that node. Such information may be in the form of a "broadcast" message intended for all nodes in the network or as a message only for the intended node with the MAC address.
Information sent over an Ethernet network is in the form of discrete packets defined according to the seven layer Open Systems Interconnection (OSI) standard maintained by the American National Standards Institute (ANSI). OSI is a layered structure in which the highest layers take advantage of the capabilities of the lower layers to send information between nodes. Information is passed between nodes in the form of discrete packets containing data or control information supplied by the various OSI layers. The highest layers are the Application layer, the Presentation layer, and the Session layer which may include Telnet, File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SNMP), and Domain Name System (DNS).
The Transport layer typically includes the Transmission Control Protocol (TCP) along with the User Datagram Protocol (UDP), among others, which provide for the delivery of the data to a desired device and the division of the information into discrete packets for sending. Received packets are reassembled in a like manner. The Network layer routes messages back and forth between a source node and a destination node according to Internet Protocol (IP) addresses by adding an IP header to each packet indicating the source and destination IP addresses. The lowest layer is the physical link layer in which the hardware MAC addresses are used.
A test instrument connected to the LAN must display complex network information gathered from the LAN, typically as a selected set of network parameters chosen to best indicate the status of critical parameters. A selected set of network parameters may include the presence of a link pulse, the percent utilization of the network capacity, the percent collisions of the network traffic, and the presence of errors on the LAN. Percent utilization is the percent of the LAN bandwidth consumed by frames, collisions, and ghosts and is often the primary yardstick for measuring overall network performance. Percent collisions is the percent of the used bandwidth consumed by collisions which characterizes how well the network is handling a given volume of traffic.
In prior art test instruments, which also include expert systems for analyzing LANs in the form of a computer operating in combination with a protocol analyzer, allow for analysis of network problems by measuring network parameters. Percent utilization and percent collisions may both be determined but are separately analyzed. However, percent utilization and percent collisions are interrelated because both normal network traffic and traffic generated as a result of collisions both consume limited network bandwidth. Interpreting one network parameter without considering the other network parameter may lead to incorrect conclusions about the overall behavior of the LAN which may collectively be understood as network health.
Network health is a composite indicator of the condition of the LAN that is based on a system of rules that take into account both percent utilization and percent collisions to provide for easier interpretation by a test instrument user. Providing a decision on network health would be particularly useful in service and maintenance applications requiring quick and useful determination of current network conditions by the instrument user. Therefore, it would be desirable to provide a method for determining various degrees of network health based on the interpretation of multiple network parameters.